The invention relates to novel sponges which have a variety of textures, structures, water absorbing properties and biodegradability. Certain sponges of the invention can be used as edibles, and there can be produced low- high and ultra-high-calorie content sponges. The latter are of special value where highly concentrated edibles are required. Certain types of sponges can be used in medicine and also in a variety of industries. Sponges according to the invention can be used in diapers, hygienic pads, packaging material and the like.
There is known a wide variety of spongy organic and inorganic materials. There are known open-cell sponges and closed-cell ones. According to the present invention there can be provided edible sponges and sponges for a variety of uses, with controlled properties.
A cellular solid is an interconnected network of solid struts or plates which form the edges and faces of cells (Gibson and Ashby, 1988). Cellular materials such as cork whose first reported use was as bungs in wine bottles in Roman times, and other similar solids have been used for centuries. Recently, a variety of man-made cellular solids have been developed. They include honeycomb-like materials, and polymeric foams which are used in everyday life for the production of disposable coffee cups for example, to construction of crash padding in an aircraft cockpit. Foaming techniques for polymers, metals, ceramics and glasses exist. These foams can be used for insulation, cushioning and absorbing the impact of kinetic energy.
The structure of cellular solids ranges from the near-perfect order of the bee""s honeycomb to the disordered, three-dimensional networks of sponges and foams (Gibson and Ashby, 1988). There is a clear distinction between open-cell edges and closed-cell foams. In the first, the solid material has been drawn into struts which form the cell edges. In closed cells, solid membranes close off the cell faces, but the solid is rarely uniformly distributed between the edges and faces. When foaming takes place, surface tension can be a dominant force responsible for drawing the solid material into the cell edges, leaving a thin cell face framed by thicker edges. If surface tension shapes the structure, four edges meet at 108xc2x0 angles at each vertex, and three faces meet at 120xc2x0. Metal, ceramic and glass foams are good examples of this type of structure.
Many foods are solid foams. Bread usually has closed cells, expanded by the fermentation of yeast or by CO2 from bicarbonate. Meringue is a foamed egg white with sugar. Foamed chocolate is an example of a food expanded to change its texture. Other hard brittle candies are also often expanded to make them attractive to consumers or if they are sold by volume, to make them cheaper. Other important xe2x80x9csolid-foamxe2x80x9d foods are breakfast cereals and snack foods, which are foamed with steam to produce texture and crunchiness.
Nussinovitch et al. (1993) have demonstrated the production of mechanically stable solid sponges by immersing bicarbonate-containing agar and alginate gels in an acid bath, causing them to form internal gas bubbles, then freeze-drying them. These sponges exhibit characteristic compressive stress-strain curves and their properties are largely dependent on the conditions of their preparation.
The invention demonstrates that it is possible to create hydrocolloid sponges, by a variety of methods. Different, unrelated techniques are described here in addition to a procedure to change the structure and porosity of sponges. Another aim of the research was to show that stress-strain relationships in sponges can be successfully described by a three-parameter model originally developed for polymeric sponges and baked goods and that these sponges, because of their different inherent properties, could have potential uses in many different fields.